Nutritional Factors Affecting the Ratio of Solvents Produced by Clostridium acetobutylicum

Fermentation of whey by Clostridium acetobutylicum yielded butanol and acetone in a ratio of approximately 100:1. This ratio amounted to only 2:1 in synthetic media with glucose, lactose, or glucose plus galactose as substrates. Removal of citrate from whey and addition of minerals resulted in an increase in the amount of acetone produced. Experiments carried out in a chemostat with a low-phosphate synthetic medium revealed that the butanol/acetone ratio could be increased from 2:1 to 3.8:1 by cofermentation of l-lactate and from 2:1 to 8:1 by iron limitation. The performance of the fermentation in a low-iron glucose medium above pH 5.1 yielded l-lactate as the main product.